Traveling wave grids with agitated surface using piezoelectric effect and acoustic traveling waves

ABSTRACT

A system for transporting particles includes a substrate and a plurality of spaced electrically conductive electrodes carried by the substrate. Further included is a carrier medium adapted for the retention and migration of particles disposed therein, wherein the carrier medium is in operational contact with the electrodes, and a vibration generator is positioned in relation to the substrate to impart vibrations into the carrier medium. In an alternative embodiment, the vibration generator is configured to generate an acoustic traveling wave, which includes a vibration component and a motivation component.

INCORPORATION BY REFERENCE

This is a divisional of and claims priority to application U.S. Ser. No.11/501,898, filed Aug. 8, 2006, entitled “Traveling Wave Grids WithAgitated Surface Using Piezoelectric Effect And Acoustic TravelingWaves”, by Baomin Xu et al., the disclosure of which is herebyincorporated by reference in its entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

This invention was made with United States Government support underCooperative Agreement No. W911NF-04-C-0040 awarded by the United StatesArmy. The United States Government has certain rights in the invention.

BACKGROUND

The present application relates to the field of traveling wave grids,and more particularly, to improving movement and control of organic,inorganic and/or biological particles being carried by the travelingwave grids to focus, separate and/or concentrate the particles.

It is desirable to move the particles for a variety of reasons. Forexample such movement is useful in applications related to, amongothers, analysis of proteins and DNA fragment mixtures, andmethodologies used for processes such as DNA sequencing, isolatingactive biological factors associated with diseases such as cysticfibrosis, sickle-cell anemia, myelomas, and leukemia, and establishingimmunological reactions between samples on the basis of individualcompounds. Movement by traveling wave grids is an extremely effectivetool because, among other attributes, it does not affect a molecule'sstructure, is highly sensitive to small differences in molecular chargeand mass, and will not damage the cells of biological materials.

Traveling wave grids manipulate particles by subjecting them totraveling electric fields. Such traveling fields are produced byapplying appropriate voltages of suitable frequency and phase toelectrode arrays of suitable design, such that non-uniform electricfields are generated.

Thus, by use of traveling wave grids, particles are manipulated andpositioned at will without physical contact, leading to new methods forfocusing, separation and concentration technology.

It has been appreciated, however, that with existing and previouslyproposed traveling wave grid devices the particles, including organic,inorganic and bio-materials, within the carrier medium, may settle andadhere to the surface of the traveling wave grid due, for example, toVan der Waals bonding, leading to loss in the amount of a sample andcompromising long term reliability.

INCORPORATION BY REFERENCE

U.S. Patent Application Publication No. US2004/0251135A1 (U.S. Ser. No.10/459,799, Filed Jun. 12, 2003), published on Dec. 16, 2004, by Meng H.Lean et al., and entitled, “Distributed Multi-Segmented ReconfigurableTraveling Wave Grids for Separation of Proteins in Gel Electrophoresis”;U.S. Patent Application Publication No. US2004/0251139A1 (U.S. Ser. No.10/460,137, Filed Jun. 12, 2003), published on Dec. 16, 2004, by Meng H.Lean et al., and entitled, “Traveling Wave Algorithms to Focus andConcentrate Proteins in Gel Electrophoresis”; U.S. Patent ApplicationPublication No. US2005/0123930A1 (U.S. Ser. No. 10/727,301, Filed Dec.3, 2003), published on Jun. 9, 2005, by Meng H. Lean et al., andentitled, “Traveling Wave Grids and Algorithms for BiomoleculeSeparation, Transport and Focusing”; U.S. Patent Application PublicationNo. US2005/0123992A1 (U.S. Ser. No. 10/727,289, Filed Dec. 3, 2003),published on Jun. 9, 2005, by Volkel et al., and entitled,“Concentration and Focusing of Bio-Agents and Micron-Sized ParticlesUsing Traveling Wave Grids”; U.S. Publication No. US 2004-0164650 A1(U.S. Ser. No. 10/376,544, Filed Feb. 25, 2003), published Aug. 26,2004, by Xu et al., and entitled “Methods to Make Piezoelectric CeramicThick Film Array”; U.S. Pat. No. 6,964,201, issued Nov. 15, 2005, by Xuet al., and entitled, “Large Dimension, Flexible Piezoelectric CeramicTapes”; and U.S. Pat. No. 6,895,645, issued May 24, 2005, by Xu et al.,and entitled, “Bimorph Mems Devices”, each hereby incorporated herein byreference in their entireties.

BRIEF DESCRIPTION

A system for transporting particles includes a substrate and a pluralityof spaced electrically conductive electrodes carried by the substrate.Further included is a carrier medium adapted for the retention andmigration of particles disposed therein, wherein the carrier medium isin operational contact with the electrodes, and a vibration generator ispositioned in relation to the substrate to impart vibrations into thecarrier medium.

In an alternative embodiment, the vibration generator is configured togenerate an acoustic traveling wave, which includes a vibrationcomponent and a motivational component.

BRIEF DESCRIPTION OF THE DRAWINGS

The present subject matter may take form in various components andarrangements of components, and in various steps and arrangements ofsteps. The drawings are only for purposes of illustrating preferredembodiments and are not to be construed as limiting the subject matter.

FIG. 1 is a schematic illustration of a preferred single sided travelingwave grid configuration.

FIG. 2 is a representative four phase traveling wave voltage patternemployed in the preferred systems and traveling wave grids.

FIG. 3 is a schematic illustration of biomolecule transport from oneelectrode to another.

FIG. 4 is a schematic illustration of a preferred embodimentelectrophoretic system utilizing distributed, reconfigurable, andreprogrammable traveling wave grids.

FIG. 5 charts the particle density for PEG coated and uncoated Siwafers, for a static soak in an ARD solution;

FIG. 6 charts particle density for PEG coated and uncoated Si wafers,for an ultrasonic soak in an ARD solution;

FIG. 7 charts particle density for PEG coated and uncoated Si wafers,for static and ultrasonic soaked material in a bacteria solution;

FIG. 8 depicts a traveling wave grid with a full piece of piezoelectricmaterial attached to the bottom surface;

FIG. 9 is a traveling wave grid with discrete pieces of piezoelectricmaterial attached to the bottom surface;

FIG. 10 depicts a traveling wave grid with a full piece of piezoelectricmaterial/dielectric layer on a top surface;

FIG. 11 depicts a traveling wave grid with discrete pieces ofpiezoelectric material and a dielectric layer on the top surface;

FIG. 12 depicts a traveling wave grid with a full piece of piezoelectricmaterial/dielectric layer on an etched area of the substrate;

FIG. 13 depicts a traveling wave grid with discrete pieces ofpiezoelectric material and a dielectric layer on an etched portion ofthe substrate;

FIG. 14 a provides a sketch of a mechanism for energy transfer from anacoustic wave (in a solid) to a block using friction contact;

FIG. 14 b is a sketch of a mechanism for energy transfer from anacoustic wave (in a solid) to a block using wave action;

FIG. 14 c depicts a sketch of a mechanism for energy transfer from anacoustic wave (in a solid) to a block, showing boundary layerinteraction;

FIG. 15 depicts a first embodiment of a structure combiningelectrostatic traveling wave and acoustic traveling wave (ATW)operation;

FIG. 16 is a second example of a structure combining electrostatictraveling wave device concepts and acoustic traveling wave (ATW)concepts; and

FIG. 17 sets forth a device using distributed piezoelectric elements tolocally change the ATW amplitude and direction in combination with anelectrostatic traveling wave grid device.

DETAILED DESCRIPTION

FIG. 1 is a single sided traveling wave grid device 100, such as anelectrostatic traveling wave grid, comprising a plate 110, a pluralityof parallel and closely spaced electrodes 112, 114, 116, and 118, and aneffective amount of a carrier medium 120, of liquid or gel disposed incommunication with the electrodes. In one design, the electrodes may beformed from platinum or alloys thereof. A thin layer of titanium may bedeposited on the plate, which may be glass, to promote adhesion betweenthe electrodes and plate. A four (4) phase electrical signal (φ1-φ4) isshown as being utilized in conjunction with assembly 100. Accordingly, afirst electrode such as electrode 112 may be utilized for a first phaseφ1 of the electrical signal. Similarly, a second electrode immediatelyadjacent to the first, such as electrode 114, may be utilized for asecond phase φ2 of the electrical signal. And, a third electrodeimmediately adjacent to the second electrode, such as electrode 116, maybe utilized for a third phase φ3 of the electrical signal. Moreover, afourth electrode immediately adjacent to the third electrode, such aselectrode 118, may be utilized for a fourth phase φ4 of the electricalsignal. The distance between the centers of adjacent electrodes isreferred to as pitch, and denoted as “p.” The width of an electrode isdenoted as “w.” And the distance between facing sidewalls or edges ofadjacent electrodes is “s.” It is to be appreciated the above conceptsmay be used to form a double sided grid assembly which employs a seconddesign similar to that as described and located so as the two surfacesare on either side of the carrier medium.

FIG. 2 is a representative four phase voltage pattern or waveform usedin the assembly 100. Specifically, FIG. 2 depicts the four phase voltagewaveform with 90 degree separation between phases. Each waveformoccurring in each phase is a square wave pulse. Each pulse issequentially applied to an adjacent electrode. Thus, a first pulse inphase φ1, is applied to a first electrode for a desired time period,such as T/4. Upon completion of that first pulse, such as at time T/4, asecond pulse in phase φ2 is applied to a second electrode, immediatelyadjacent to the first electrode. Upon completion of that second pulse,such as at time T/2, a third pulse in phase φ3 is applied to a thirdelectrode, immediately adjacent to the second electrode. Upon completionof that third pulse, such as at time 3T/4, a fourth pulse in phase φ4 isapplied to a fourth electrode, immediately adjacent to the thirdelectrode. This sequential and ordered array of voltage pulsing resultsin organic, inorganic or bio-material particles dispersed in the liquidto “hop” from the vicinity of one electrode to another. The synchronousmode of propagation is depicted in FIG. 3 and may be described as a“hopping” mode where the organic, inorganic or bio-material particleshop from electrode to electrode in the direction of the pulse train. Thetransit time to migrate across the dielectric space is then given by:

t _(transit) =s/μE,

where pitch is given by p=w+s, and w and s are the electrode width anddielectric space, respectively. Electric field and mobility are given byE and μ, respectively. The period for one cycle through the four phasesis 4*t_(transit), so that the maximum sweep frequency is:

f<μE/4s.

For sustained transport, the organic, inorganic or bio-materialparticles have to have sufficient speed (μE) and time (t_(transit)) totraverse the distance of the dielectric space, s. This equation impliesthat for sustained transport, there is a critical frequency for organic,inorganic or bio-material particles of a certain mobility. Therefore, bystarting with the highest operational frequency, one can progressivelyscan downwards in frequency until the organic, inorganic or bio-materialparticle of the right mobility starts to move. This means that forcertain organic, inorganic or bio-material particles, the fastest (andlowest molecular weight) particles, e.g. bio-molecules, may be separatedout from the sample one at a time. The preceding discussion describesone particular use of the wave grid.

The present concepts, however, provide significant opportunity for otheruses, as well as innovation in the design of specific systems oftraveling wave grids to focus, separate, and concentrate organic,inorganic and bio-material particles. One strategy is to fabricate thesmallest pitch possible for the traveling wave grids for maximumflexibility in reconfiguring the grids for specific applications. FIG. 4is a schematic illustration of an electrophoretic traveling wave gridsystem (device) 200 utilizing multiple distributed, reconfigurable, andreprogrammable traveling wave grids. Specifically, the multi-segmentedtraveling wave grid system includes a first grid segment 210, a secondgrid segment 220, and a third grid segment 230. As will be appreciated,each segment includes a plurality of parallel and closely spacedelectrodes. Two contiguous pads on respective sides together offerconnection to the four phase circuit through one or more buses 240, 250,and 260. The system 200 preferably further includes one or moreprogrammable voltage controllers such as controllers A, B, and C. Aswill be appreciated, the controllers are in electrical communicationwith the traveling wave grid (or segments thereof) through the notedbuses.

In utilizing system 200, one particular strategy involves movingorganic, inorganic or bio-material particles of interest onto individuallocal traveling wave grid segments using controller A where they arethen available for subsequent processing using controllers B, C and soforth. Each controller may be a separate peripheral interface controller(PIC) implementation or a single PIC with multiple pre-programmedinstructions. For example, in operation, system 200 of FIG. 4 may beutilized to separate a sample of various bio-molecules (of bio-materialor other type of particles) as follows. A sample 270 is deposited ontothe grid segment 210. The sample migrates to region 272 and continues tomigrate onto adjacent grid segment 220. Operation of system 200continues until a region 274 of bio-molecules forms within grid 220.Depending upon the bio-molecules and grid parameters, the bio-moleculesconstituting region 274 may further migrate to adjacent grid segment230, and form a region 276 of bio-molecules. Generally, this strategyutilizes an initial separation using a first controller and secondaryrefinements or further separation using other controllers and segmentsof grids. Secondary refinements include further concentrating ofmigrated bio-molecules and focusing of bands or patches.

The traveling wave grid devices described above, and in the aboveincorporated materials, may be used in connection with a number ofoperations and are effective in translating a carrier medium within alayer of thickness equal to 5 times the spatial pitch of the travelingwave grid.

An issue, with the previously described traveling wave grid devices isthe adhesion of organic, inorganic and bio-material particles containedin the carrier medium, to surfaces of the traveling wave grid devices.Such adhesion may occur due to Van der Waals bonding for particles whichhave fallen to a device surface. This adhesion will lead to loss in theamount of sample material and compromise long-term reliability.

One way to address the adhesion issue is to employ specialized coatings,to form enthalpic or entropic barriers to decrease particle adhesion.Another possible procedure to reduce adhesion is by use of low amplitudevibrations, such as signals at ultrasonic or other appropriatefrequencies.

Anti-adhesion through the use of surface coating of substrates has beenreported in the literature not just for different types of cells andbacteria but also for proteins and therefore simulants for viruses andtoxins. Follstaedt et al. studied the absorption of bovine serum albumin(BSA) on silicon wafers coated either with a hydrophilic PolyethyleneGlycol (PEG) surface for 24 hours with a 0.1 mM solution of BSA, foundthat both types of monolayers reduced the adsorption of protein comparedto the bare Si surface. In addition, the adsorbed protein layer measuredby ellipsometry was thinnest in the case of the PEG surface coating.(See, Follstaedt, S. C., Last, J. A., Cheung, D. K., Gourley, P. L.,Sasaki, D. Y., “Protein adhesion on SAM coated semiconductor wafers:Hydrophobic versus hydrophilic surfaces” Sandia Report, SAND2000-3016(2000)).

Zhang et al. studied the adsorption rates of BSA and two different humancell lines (lung fibroblast and epithelial cells) on PEG coated siliconsurfaces as a function of exposure times. Their experiments showed astrong increase in adsorption within the first 10 minutes, and a veryslow increase thereafter. They found that after 2 hours the reductionsof BSA, epithelial and fibroblast cell adsorption onto PEG treatedsurfaces compared to untreated silicon surfaces were 76%, 82%, and 64%,respectively. (See, Zhang, M., Desai, T., Ferrari, M., “Protein andcells on PEG immobilized silicon surfaces”, Biomaterials, 19, 953-960(1998)).

Kingshott et al. reported improvements in reducing adhesion of aGram-negative Pseudomonas sp. on PEG coated surfaces as compared tocontrols. They also showed that such reductions are only possible if thePEG layer is covalently bonded to the substrate. It was speculated thiswas necessary to overcome the possible deleterious biodegradationmechanisms that opportunistic bacteria use to colonize surfaces. Anotherpossible reason for the poor anti-adhesion properties of non-covalentlybound PEG is its hydrophilic nature which allows it to dissolve into thebuffer solution over time. Also, due to its synthetic nature, PEG is apoor food source for bacteria, thus reducing the risk of bacterialpotentiation or virus transmission. (See, Kingshott, P., Wei, J.,Bagge-Ravn, D. Gadegaard, N., Gram, L., “Covalent Attachment ofPoly(ethylene glycol) to Surfaces, Critical for Reducing BacterialAdhesion” Langmuir, 19, 6912-6921 (2003)).

To verify the effectiveness of specialized coatings and ultrasonicenergy from stopping particles from bonding and/or adhering to travelingwave grid surfaces, and removing particles which have become boundand/or adhered, applicants performed preliminary proof of conceptexperiments which tested for particle amounts on the surface of coatedand uncoated substrates in static and ultrasonic baths.

In connection with these experiments, it is considered that PolyethyleneGlycol (PEG) self-assembled monolayer coatings on SiO2 surfaces willreduce bacteria adhesion compared to uncoated samples. However, and aswill be seen by the following experiments, although coating of thesubstrate does increase anti-adhesion, greater anti-adhesion behavior isobtainable. In addition, while a particular surface coating may beeffective for one type of particle, other particles, may behavedifferently. In the following experiments, applicants use Arizona RoadDust (ARD), which is Arizona sand ranging in size from approximately 1to 20 μm diameter, and which has been used for many years in testing ofproducts and processes such as air filters, etc. Other names by whichthe sand is known is Arizona Silica, AC Fine and AC Coarse Test Dust,SAE Fine and Coarse Test Dusts, J726 Test Dusts, among others.

In order to attempt to improve anti-adhesion, the present experimentsfurther applied ultrasonic energy to the substrates. The effectivenessof this process was first tested on Si wafers.

The experimental protocol employed three different liquid baths to testthe effect of ultrasonic bath energy. The liquids were de-ionized (DI)water, bacteria solution, and ARD solution. The substrates used in theexperiments were 4″ Si wafers with and without PEG coatings. Theeffectiveness of this method was measured using a KLA-Tencor Surfscan4500 (from KLA-Tencor Corporation), which allows for an automatic scanusing a laser to detect surface particles. Because the tool cannotdistinguish between bacteria and ARD, it detects and counts allparticles on the surface, and determines the effective cross-sectionalarea of the particles. Also the entire wafer is scanned providing datafrom a large surface area. As for the ultrasonic tool, a LR Quantrax210H Ultrasonic Bath (from L. R. Quadrex Corporation) was used with asetting of 43 kHz and 135 watts. All soaks with and without ultrasoundwere done in a Petri dish with 60 to 80 ml of liquid.

The PEG coating was covalently bound to the silicon wafer usingN-(triethoxysilylpropyl)-Opolyethylene oxide urethane (which may beobtained, for example, from Gelest Inc.). The silicon wafer was soakedin a solution of 60 ml Toulene, 0.5 ml Hexylamine, and 1.0 ml PEG for 30minutes. After the soaking the wafers were thoroughly rinsed withtoluene, acetone, and isopropyl alcohol (IPA).

An ARD solution of 0.01 gm/ml was used and 2 ml of the solution wasadded for every 60 ml of H₂O. A concentrated solution of B.thuringiensis suspended in tap water was used as the bio-agent B.anthracis simulant. Twenty mL of the solution was added to 60 ml of H₂O.All wafers were thoroughly rinsed with water and blown dry with N₂ aftereach soak.

In a first part of the experiment, Arizona Road Dust (ARD) solutionswere used to determine the effect of static and ultrasonic agitationtreatment on PEG coated and non-PEG coated Si wafers. Three wafers werelabeled PEG-21, PEG-22, and Si-25. PEG-21 and PEG-22 refer to the PEGcoatings prepared on separate occasions and Si-25 was a bare siliconwafer.

FIG. 5, presents the results for static tests, i.e., without use of anultrasonic bath, and FIG. 6 provides data for the ultrasonic soak tests.All soaks were for 5 minutes and particles greater than 6 μm² in areawere counted using the Surfscan 4500 wafer particle counter (fromKLA-Tencor Corporation). Particle densities before and after soakingwere compared.

The chart of FIG. 5 verifies the static bath allowed particles to settleand adhere to the Si wafer. The largest particle accumulation was on theuntreated bare silicon wafer (Si-25) where the particle densityincreased by ˜5 counts/mm². As for the PEG treated silicon wafers(PEG-21 and PEG-22), the particle increase was much less, onlyincreasing the density by ˜1 count/mm². Thus, the experiments showed thePEG coated samples (PEG-21 and PEG-22) performed better than theuntreated wafer (Si-25).

In contrast to the increase of particle counts after the static soak (asshown in FIG. 5), the particle counts, as shown in FIG. 6, decreasedafter soaking in the ultrasonic bath. Effectively, the ARD solutionultrasonic bath did not result in any additional particles for both thePEG coated (PEG-21 and PEG-22) and uncoated (Si-25) samples.

Turning to tests reflected by the results shown in FIG. 7, wafers soakedin bacteria solutions for 30 minutes were measured for particles. Anuntreated Si wafer (Bare Silicon) and a PEG treated Si wafer (PEGCoating) were soaked under static conditions. Additionally, a PEGtreated Si wafer was tested in an ultrasonic bath with the bacteriasolution (PEG Coating+Ultrasonic). FIG. 7 illustrates before and aftersoak measurements of the three different conditions. As shown, theuntreated Si wafer had the highest particle density increase of ˜38counts/mm². The PEG coated wafer had an increase of ˜29 counts/mm² andthe PEG coated ultrasonic bath wafer had an increase of only of ˜5counts/mm². As can be seen by the results, adding the ultrasonic bathincreased the anti-adhesion effects.

Further experiments on comparing different PEG coatings confirm that,among commercially available PEG formulas, e.g. PEG4-6 (a short chainpolymer) and PEG6-9 (a long chain polymer), and a mixture preparedin-house of 50:50 PEG4-6 and PEG6-9, the PEG4-6 performed best in theanti-adhesion tests. One explanation for better performance may beimproved surface coverage with PEG4-6. If contact angle is an indicationof film coverage, then higher wetting angles from PEG4-6 coatings wouldsuggest better surface coverage.

The ultrasonic bath and static bath experiments showed thatanti-adhesion performance is improved with an applied ultrasonic energyto the surface of a Si wafer, and that it would be difficult to preventARD adhesion using PEG surface coatings alone. The ultrasonic approachhas been shown to improve prevention of ARD adhesion. It has also beendetermined the combination of a coated surface along with ultrasonicenergy improves anti-adhesion of ARD and bacteria.

The above experiments verify that using ultrasonic bath can improve thesurface anti-adhesion, but the bulky ultrasonic bath can not easily bedirectly integrated with the traveling wave grid device as shown in FIG.1 or 4 to form a compact or portable device. The use of ultrasonic bathis basically to apply ultrasonic energy to the liquid and the substrateto generate mechanical vibrations, in principle if other methods can beused to generate similar vibrations, the same anti-adhesion effect canbe reached. Thus, attention is now directed, to FIG. 8, whichillustrates a traveling wave grid device 300 incorporating a verticalvibration generator. Traveling wave grid device 300, shown in asimplified side view, has components similar to that discussed inconnection with FIGS. 1 and 4. Particularly, a substrate made from glassor other insulating material 310 carries a plurality of traveling waveelectrodes 312 (the power connections are not shown for convenience ofexplanation). In addition to the components of existing traveling wavegrid devices, this embodiment further includes a piezoelectric material314 having electrodes 316, 318 located under glass substrate 310. Inthis embodiment, piezoelectric material 314 is a continuous sheet ofpiezoelectric material, such as ZnO, piezoelectric polymers, orpiezoelectric ceramics. An energization (e.g., power) source 320 isconnected to electrodes 316, 318 of piezoelectric material 314. Byactivation of power source 316, piezoelectric material 314 will becomeenergized, causing vertical vibrations 322 to be directed toward andthrough the surface of glass substrate 310, and into carrier medium 328.By this arrangement, particles, such as particles 324 and 326 withincarrier medium 328 are intersected and affected by vertical vibrations322. Particularly, particles 324 suspended within carrier medium 328,and do not come into contact with the surface of traveling wave griddevice 300. In this situation, the vertical vibration 322 generated bypiezoelectric material 314 and power source 320, which may be consideredcomponents of the vertical vibration generator, stop particles 324 fromcoming into contact with the surface of device 300. Thus, the verticalvibration components act to eliminate contact between the surface andthe particles from occurring. Additionally, in situations whereparticles have adhered to the surface of device 300, vertical vibrations322 act to remove such particles 326 by, for example, breaking the Vander Waals bonds. Thus integrating the vertical vibration components(314, 316, 318, 320) into the traveling wave grid device 300, permitsnot only the breaking of bonds between particles and the surface ofdevice 300, but also prevents contact between particles 324 within themedium 328 and surface of device 300.

Turning to FIG. 9, illustrated is another traveling wave grid device400, including substrate 410 made from glass or other insulatingmaterials and traveling wave electrodes 412, which also incorporates avertical vibration generator located on the bottom surface of thetraveling wave grid device 400. The embodiment employs discrete piecesof piezoelectric material 414 having electrodes 416, 418. Electrodes 416are connected together as a common current return path and connected tothe power source 420. Each of the discrete pieces of piezoelectricmaterial 414 also includes a corresponding discrete electrode 418. Thisarrangement permits selected connection of electrodes 418 to a powersource 420, which in turn permits for selective energization of thediscrete pieces of piezoelectric material 414. Thus, a distinctionbetween the devices of FIG. 8 and FIG. 9, is that upon application ofpower by power source 320 of FIG. 8, vertical vibrations occur over thelength of the traveling wave grid device 300. However, operation oftraveling wave grid device 400 of FIG. 9 permits this embodiment toallow distributed and local control of vibrations for the traveling wavegrid.

As will be expanded upon below, the continuous sheet of piezoelectricmaterial 314 of FIG. 8 and the discrete pieces of piezoelectric material414, may be attached or grown on the substrates 310, 410. The substratesmay have a surface conductive layer, on the bottom surface, which worksas part of the electrodes of the piezoelectric material or makes theconnection of the piezoelectric material to the power source moreeasily. Also, in some cases, the surface of the devices may beconsidered the top surfaces of the electrostatic traveling wave griddevice described above and in the following may be considered the topsurfaces of the substrates and/or electrodes, or in other designs, whenthere is a protective cover such as a PEG covering (not shown), thesurface may be made of this material.

Turning now to FIGS. 10 and 11, in addition to having piezoelectricmaterial on the bottom surface of the traveling wave grid device, it isalso possible to attach or grow piezoelectric material on the topsurface of the traveling wave grid device. For example, as shown by theembodiment of FIG. 10, a traveling wave grid device 500 is built with aglass substrate 510 and electrodes 512, as in previous designs. However,in this configuration piezoelectric material (ZnO layer or PZT layer)514 (with electrodes 516, 518) is located on a top surface of the glasssubstrate 510.

After attaching or growing the piezoelectric material layer 514, a thindielectric layer 519, such as Parylene, silicon oxides or siliconnitrides or other appropriate material is deposited to isolate operationof the vertical vibration generator from traveling wave grid electrodes512. Traveling wave electrodes 512 are formed on the surface ofdielectric layer 519. Electrodes 516, 518 are connected to a powersource (not shown) by extending conductive lines (not shown) from theelectrodes 516, 518 at edges of the device. Thus, the embodiment of FIG.10 discloses a continuous sheet of piezoelectric material on the topsurface of the traveling wave grid device.

Turning now to FIG. 11, depicted is another embodiment, similar to FIG.10, but where the traveling wave grid device 600, having the glasssubstrate 610 and traveling wave electrodes 612, uses several discretepieces of piezoelectric material 614 (and electrodes 616 and 618) on thetop surface of the traveling wave grid device. A thin dielectric layer619 is deposited onto the piezoelectric material 614. In this design,the electrodes 616, 618 are connected to a power source (not shown) byconductive lines (not shown) extending out from sides of the device.Particularly, the conductive lines may extend out of the page.

In both embodiments of FIGS. 10 and 11, vertical vibrations aregenerated such as discussed in connection with FIGS. 8 and 9, to bothstop particles from contacting the surface of the traveling wave griddevice, and for breaking bonds holding particles to the surface of suchdevice. Also, while power sources and connections are not shown in FIGS.10 and 11, they are similar to those shown in FIGS. 8 and 9.

Depending on the application, thin film, thick film or bulkpiezoelectric materials can be used, but a specific embodiment could bethe use of thick films. In this embodiment, the thick films may bedeveloped by a screen printing laser transfer process, such as taught inU.S. Publication No. US 2004-0164650 A1, published Aug. 26, 2004; U.S.Pat. No. 6,964,201, issued Nov. 15, 2005; and U.S. Pat. No. 6,895,645,issued May 24, 2005, each previously incorporated herein by reference intheir entireties, which allows for the transfer of discrete orcontinuous piezoelectric material such as PZT (lead zirconate titanate)thick film elements on the glass at very low cost.

The piezoelectric constant d33 of laser transferred PZT is about 300pm/V or higher. Generally, a surface displacement of about 10 nm issufficient to break Van der Waals bonding. Thus using about 30V to 40V,a surface displacement of 9 to 12 nm (using longitudinal mode) can begenerated, which is sufficient surface agitation to achieve the desiredde-bonding results. Applying 30V to 40V driving voltages to thepiezoelectric material are fully acceptable for the traveling wavedevice. For one conventional embodiment, the thickness of the lasertransferred PZT thickness is between 10 μm to 50 μm, and preferably 10μm or, alternatively, about 50 μm.

The longitudinal resonant frequency of 50 μm-thick PZT is about 40 MHz.Thus, the vertical vibrations will operate at far below the resonantfrequency, such as below 10 MHz, so that transfer of too large ofvibrations and/or excessive mechanical energy into the carrier mediumwill be avoided. Again, if too large of vibrations and/or excessivemechanical energy are input to the carrier medium, this may damage ordestroy the bio-materials in the carrier medium. Thus PZT elements willbe operated under static condition and their displacement will in oneembodiment not change with frequency but will linearly increase with adriving voltage. Depending on the specific organic, inorganic orbio-material particles, under the static driving condition, the drivingvoltage and frequency can be tuned to reach an optimized surfacevibration, which will provide an optimal effect for specific organic,inorganic or bio-material particles.

Turning to FIG. 12, illustrated is another traveling wave grid device700, having a substrate 710 and traveling wave electrodes 712, and whichalso employs a vertical vibration generator to reduce particles fromcontacting or and/or adhering to the surface of the traveling wave griddevice. While this embodiment shares many of the same attributes of theprevious embodiment of FIG. 10, a distinction is that the glasssubstrate 710 is etched to have a recessed area 710 a. It is within thisrecessed area 710 a that piezoelectric material 714 is either depositedor grown. Piezoelectric material 714 has associated piezoelectricelectrodes 716 and 718, which in one embodiment may be connected to apower source (not shown) by conductive lines which come out of thedevice at angles such as into and out of the page. Of course, otherconnection schemes may be used as would be known to one of ordinaryskill in the art. A planarizing and/or dielectric material 719 isprovided over piezoelectric material 714 and glass substrate 710 suchthat a planarized surface is presented on which the traveling wave gridelectrodes 712 are formed. By this embodiment, a planar surface ispresented for the electrodes, increasing the manufacturability of thepresent design.

Turning to FIG. 13, another traveling wave grid device 800 is presented.In this design, and similar to FIG. 12, substrate 810 is manufactured toinclude a recessed area 810 a. Thereafter, individual piezoelectricpieces 814 are attached or grown within recessed area 810 a. Similarly,electrodes 816 and 818 are provided, and connections made, such that thepieces of piezoelectric material 814 may be controlled by a power source(not shown). After the piezoelectric pieces 814, electrodes 816, 818 andassociated connections have been located within the etched area 810 a,planarization and/or dielectric material 819 is provided over thepiezoelectric material and glass substrate to permit the formation ofthe traveling wave grid electrodes 812.

Turning now to operation of the described traveling wave grid devices ofFIGS. 8-13. Typically such devices are operated in several stages.During an initial system flush of a previous tested sample, thevibrations are tuned to a maximum value to dislodge any debris. Thesystem is then primed and the sample volume is introduced. During aconcentration or operational stage, the vibrations are set to acontinuous, lower-than-maximum-value setting to prevent particles fromsettling to the surface and adhering thereto, and to dislodge attachedparticles. When the composition of the particles in the carrier mediumare known, and the known particles are understood to react mostoptimally at a particular frequency and/or voltage, or an optimal rangethereof, the power sources can be set at an appropriate frequency and/orvoltage. On the other hand, if such optimal values are not known, thepower source can be varied so that multiple levels of vibrations areprovided.

The current concepts permit for compact devices compared to bulkyultrasonic baths. Also, since the traveling wave grid surface is beingvibrated to break the Van der Waals bonding and to prevent settlement ofparticles, it works for many different materials, including organic,inorganic and biological. Typically a special surface coating layer(e.g., PEG) will only work on specific bio-agents. Thus, a combinationof surface coating and applied vibrational energy enhances and improvesanti-adhesion performance for all particles in a carrier medium.

As a further improvement, the following discussion discloses processesand devices which not only eliminate and/or reduce adhesion, but alsopermit for the adjustment or modification of the movement of the carriermedium. This additional capability is achieved by the use of an acoustictraveling wave (ATW).

The following discloses the generation of an acoustic traveling wave(ATW) on the surface of the traveling wave grid using piezoelectricmaterials, which travel along the surface co-planar with theelectrostatic traveling wave grid. The ATW includes two functions toenhance operation of the device: (1) it generates vibrations on thetraveling wave grid surface that can be used to prevent sedimentation orsettlement of particles and acts to break Van der Waals bonds betweenthe traveling wave grid surface and the particles; and (2) the ATWdirection can be designed to move with or against the traveling wavegrid in order to enhance or reduce particle transport capabilities.

It is known when an acoustic (or mechanical) traveling wave is generatedon a surface and/or bulk of a solid it will transfer energy to theenvironment. Depending on the boundary condition or contact with theenvironment this energy generates different movements in theenvironment. Shown in FIGS. 14 a-14 c are the illustrations ofmechanisms for energy transfer from an acoustic wave in a solid 900 to ablock 910. In FIG. 14 a, block 910 has a friction contact (e.g. apressure on the block) with solid 900. Surface particles (not shown) ofthe solid 900 have a retrograde elliptic motion, giving them ahorizontal velocity at the peak of acoustic wave 920. This ellipticmotion is opposite to the wave motion and causes block 910 to move inthe opposite direction 930 of the wave propagation direction 940.

FIG. 14 b illustrates a wave-action mechanism, again with a solid 900 a,where block 910 a is corrugated with the same period as the acousticwave 920 a of solid 900 a, so block 910 a will move along the samedirection 930 a as the wave propagation 940 a with roughly the samephase velocity of acoustic wave 920 a. Turning to FIG. 14 c, shown is aboundary layer interaction condition. In this arrangement, solid 900 bis again arranged with block 910 b. However, here acoustic wave 920 bacts as the boundary of viscous fluid 950 b and radiates acoustic energyinto the fluid, so the fluid will move along the same direction ofacoustic wave 920 b. Thus, block 910 b on fluid layer 950 b, causes theblock to also move along the same 930 b as acoustic wave 940 b.Experimentation has shown that with the use of a “lamb-wave” membranedevice consisting of 1 μm-thick ZnO, 0.4 μm-thick Al, and 2 μm-thicksilicon nitride, the speed of the block (e.g., there is air between theblock and the membrane) can reach more than 18 mm/s.

One reason to study the preceding energy transfer mechanisms is in thedevelopment of ultrasonic motors. The case in FIG. 14 b is verydifficult to realize in real world applications, but the case shown byFIG. 14 a can effectively transfer force from the solid (which will be astator in an ultrasonic motor) to the block (which would be a part ofthe rotor in an ultrasonic motor). More particularly, FIG. 14 aillustrates the most popular design for an ultrasonic motor and has beenstudied extensively. For the case shown in FIG. 14 c, while it can alsotransfer movement from the solid to the fluid and to the block, whichmeans the ultrasonic motor with a fluid coupling between the stator andthe rotor can also be developed, it does not effectively transfer forcefrom the solid to the block.

Returning to traveling wave grid devices, such as those taught indocuments discussed and/or incorporated herein by reference, disclosedare devices which permit focusing, separation and/or concentration oforganic, inorganic and bio-material particles which are effective intranslating fluid within a layer of thickness equal to 5 times thespatial pitch of the traveling wave grid. As has been mentioned above,in these devices, particles, especially bio-materials, in the carriermedium may sediment out and adhere to the traveling wave grid surfacecausing loss in sample concentration and compromising reliability.Several methods have been discussed to reduce this adhesion, such asusing special coatings and/or piezoelectric induced vertical vibrationsto agitate the particulates. However, these elements and methods areused to just reduce the amount of adhesion of the particulates to thetraveling wave grid surface, but they do not adjust or modify thetransport of particulates in the carrier medium.

In the following discussion, further disclosed are devices and methodswhich also generate acoustic traveling waves (ATW) on the surface of thetraveling wave grid using piezoelectric effect, which travels along thesurface co-planar with the traveling wave grid. In this way not onlywill the surface vibrations be used to prevent sedimentation orsettlement of particles and break Van der Waals bonds between thetraveling wave grid surface and particles, the ATW direction may bedesigned to move with or against the traveling wave grid so as toenhance or reduce carrier medium and particle transport capabilities.One mode of usage is similar to the case shown in FIG. 14 c. In anadditive mode, the ATW will enhance the carrier medium delivery andimprove efficiency of traveling wave grid devices. Stated another way,the ATW introduces another mechanism to help in more effective particletransport. This may improve the utilization of traveling wave griddevices as to bio-material in high viscosity or gel-like media.

Theoretically, any method or structure which can generate ATW on thesurface of a traveling wave grid can be employed in the presentconcepts. As most of the acoustic traveling waves are generated by usingpiezoelectric materials, several such examples are given to generate ATWon the surface of a traveling wave grid. These structures can beclassified into two categories: generating bulk acoustic traveling wavewhich includes surface movements, and generating only surface acoustictraveling wave. Of course, any other structures, such as many structuresused in ultrasonic motors, can also be used.

Depicted in FIG. 15 is a side view of a traveling wave grid device 1000which can generate ATW in and on the traveling wave grid, while alsominimizing particle contact adhesion to the surface of the travelingwave grid. A substrate 1010 made from glass or other materials carriestraveling wave grid electrodes 1012. Ends of the glass substrate arebonded to or have grown thereon to piezoelectric sections 1016 (withelectrodes 1018, 1020) and 1022 (with electrodes 1024, 1026), with onepiezoelectric section (e.g., 1016) used as a generator and the otherpiezoelectric section (e.g., 1022) used as an absorber. Whenpiezoelectric section 1016 is used as a generator, a voltage via powersource 1028 is applied, generating a mechanical vibration. Thismechanical vibration generates acoustic wave 1025 (in glass substrate1010, but shown in the figure below glass substrate 1010, for clarity)which travel from left to right 1030, and the other piezoelectricsection 1022 absorbs the acoustic energy. That is, the acoustic(mechanical) energy is transformed to electric energy and consumed byresistance network 1032. As there is no acoustic wave reflected from theright end, an ATW 1025 is generated in glass substrate 1010, whichenhances the delivery of the carrier medium from left to right 1030. Inparticular, the ATW wave 1025 moves in the same direction as the flowdirection 1034 caused by operation of the traveling wave grid. Reversingdirections and polarities (e.g., power source 1028 is on the right-handside and resistance network 1032 is on the left-hand side) cause the ATW1025 to act in the opposite direction (e.g., see 1030 a), and thecarrier medium delivery will be reduced.

In particular, the motivation of the ATW 1025 will be acting against(e.g., 1030 a) the flow direction 1034 generated by the traveling wavegrid operation. When the ATW travels in the traveling wave grid area, italso generates surface vibrations as previously discussed, which areused to prevent settlement or sedimentation of particulates, and tobreak the Van der Waals bonding between the traveling wave grid surfaceand particles.

Shown in FIG. 16 is an embodiment for a traveling wave grid device 1100,which employs a surface launched acoustic wave to generate an ATW wave1112 only on the surface of the traveling wave grid. In order togenerate surface ATW wave 1112, a piezoelectric material 1114 such as aZnO thin film is deposited on a substrate 1116 such as glass. Theninter-digitated (IDT) electrodes 1118, 1120 are formed on both ends ofpiezoelectric film 1114, and traveling wave grid electrodes 1122 areformed on piezoelectric film 1114. If it is necessary (e.g., forisolation), a thin insulating/dielectric film (not shown) such asParylene or silicon oxide/nitride film may be deposited on the surfaceof the piezoelectric film before fabricating traveling wave gridelectrodes 1122, so that the voltage applied by a voltage source (notshown) on the traveling wave grid will not affect the operation of thepiezoelectric film. Using the IDT electrodes 1118 on the left endconnected to power source 1124 as the generator and the IDT electrodes1120 on the right end connected to resistance network 1126 as theabsorber, a continuous surface acoustic traveling wave can be generatedwhich enhances the fluid delivery from the left side to the right side.Reversing the directions and polarities, as discussed in FIG. 15, willresult in a 180 degree flip in directionality.

Turning to FIG. 17, instead of generating a homogenous ATW over theentire electrostatic traveling wave grid area, a device such astraveling wave grid device 1200 can be designed where the traveling wavegrid area also selectively overlaps with sub-areas of piezoelectricelements with distributed addressing and control. With more particularattention to traveling wave grid device 1200, similar to previousembodiments, provided is glass substrate 1210, on which are locatedtraveling wave grid electrodes 1212. However, in this embodiment,distributed piezoelectric elements are used to locally change the ATWamplitude and direction. More specifically, power source 1214 isconnected to piezoelectric element 1216 via electrodes 1218 and 1220.Activation of power source 1214 generates an ATW wave 1222, which isreceived by an absorption network comprising piezoelectric element 1224,having electrodes 1226 and 1228, connecting the piezoelectric element1224 to a resistance network 1230. By this design, the mechanicalvibrations which generate the ATW wave 1222 are transformed intoelectrical energy by the piezoelectric element 1224, and consumed byresistance network 1230.

With continuing attention to FIG. 17, oppositely positioned generatorsand absorption networks are illustrated. For example, piezoelectricelement 1232 having electrodes 1234 and 1236 is operationally connectedto power source 1238. Then, a spaced absorption network consisting ofpiezoelectric element 1240 with electrodes 1242 and 1244 connected toresistance network 1246 act to absorb ATW wave 1248 generated bypiezoelectric material 1232. As can be seen by FIG. 17, ATW wave 1222travels in the same direction as the flow direction 1250 created by thetraveling wave electrodes. On the other hand, ATW wave 1248 travels inthe opposite direction. Thus the ATW intensity (amplitude) andpropagation direction can be controlled locally, so that themanipulation ability of the device can be fine-tuned locally.

The above has been described with reference to the preferredembodiments. Obviously, modifications and alterations will occur toothers upon reading and understanding the preceeding detaileddescription. It is intended that the descriptions be construed asincluding all such modifications and alterations insofar as they comewithin the scope of the appended claims or the equivalents thereof.

It will be appreciated that various of the above-disclosed and otherfeatures and functions, or alternatives thereof, may be desirablycombined into many other different systems or applications. Also thatvarious presently unforeseen or unanticipated alternatives,modifications, variations or improvements therein may be subsequentlymade by those skilled in the art which are also intended to beencompassed by the following claims.

1. A system for transporting particles in a carrier medium adapted forretention and migration of the particles, said system comprising: asubstrate; a travelling wave grid, including a plurality of spaced,electrically conductive electrodes carried by the substrate, wherein theelectrodes carried by the substrate are part of a surface of thetraveling wave grid which generates an acoustic traveling wave; at leastone vibration generator positioned in relation to the substrate toimpart vibration to the carrier medium; and at least one absorberpositioned in relation to the substrate to absorb at least a portion ofthe acoustic travelling wave.
 2. The system of claim 1 wherein the atleast one vibration generator and the at least one absorber include apiezoelectric material.
 3. The system according to claim 2 wherein thepiezoelectric material is divided into sub-areas, at least one of thesub-areas being part of the at least one vibration generator and atleast one other of the sub-areas being part of the at least one absorber4. The system according to claim 3 wherein the sub-areas further includedistributed addressing and control.
 5. The system of claim 4 wherein theat least one vibration generator and the at least one absorber arepositioned and configured to act as a pair.
 6. The system of claim 5,wherein there are a plurality of vibration generator and absorber pairs.7. The system of claim 1 wherein the at least one absorber is connectedto a resistive network.
 8. The system of claim 1 wherein the at leastone vibration generator is connected to a power source.
 9. The system ofclaim 1 wherein the traveling wave grid employs a surface launchedacoustic ware to generate an acoustic traveling wave only on the surfaceof the traveling wave grid.
 10. The system of claim 2 wherein thepiezoelectric material has a thickness of between about 10 μm to 50 μm.11. The system according to claim 1 wherein the agitation of thetraveling wave grid surface creates about a 9 nm to 12 nm displacementbetween the traveling wave grid surface and the liquid carrier medium,which is of a sufficient amount to prevent settlement or sedimentationof particles, and to break Van der Waals bonding between the travelingwave grid surface and the particles.
 12. The system according to claim 1wherein the vibration generator includes a plurality of distributedpiezoelectric elements
 13. The system according to claim 12 wherein theplurality of distributed piezoelectric elements provides localizedcontrol of vibrations to the traveling grid surface.
 14. The systemaccording to claim 12 wherein the plurality of distributed piezoelectricelements are located on a bottom surface of the substrate.
 15. Thesystem according to claim 12 wherein the plurality of distributedpiezoelectric elements are located on an upper surface of the substrate.16. The system according to claim 1, wherein the at least one vibrationgenerator includes a continuous piece of piezoelectric material locatedon a lower surface of the substrate.
 17. The system according to claim1, wherein the at least one vibration generator includes a continuouspiece of piezoelectric material located on an upper surface of thesubstrate.
 18. The system according to claim 1, wherein the at least onesubstrate includes a recessed portion in which at least one component ofthe at least one vibration generator is located.
 19. A method fortransporting particles in a carrier medium adapted for retention andmigration of the particles, the method comprising: motivating thecarrier medium by use of a traveling wave device having a plurality ofspaced, electrically conductive electrodes carried on a substrate, thetraveling wave device being activated by application of energy to theplurality of spaced, electrically conductive electrodes; and generatingvibrations to the carrier medium being motivated, by a vibrationgenerator, wherein the vibrations act to at least one of maintainparticles in the carrier medium from making contact with a surface ofthe traveling wave device or breaking a bond between particles on thesurface of the traveling wave device.
 20. The method according to claim19 further including absorbing, by an absorber, at least a portion of anacoustic travelling wave generated by the travelling wave device.